Due to changing government requirements, specifically the Montreal Protocol, which regulate the use of ozone-depleting materials, the primary blowing agent currently being used by the industry (in the United States) for applications where good insulating properties are needed is HCFC-141b. However, the Montreal Protocol dictates that this material may not be used in the United States after 1 Jan. 2003. (HCFC-141b must be phased out of Japan by 2004; phase out dates for other countries vary from 2010-2040.) Potential replacements, the `third generation` blowing agents, are partially hydrogenated fluorocarbons (HFCs) and some hydrochlorofluorocarbons (HCFCs) and include compounds such as HFC-134a, HFC-236ea, HFC-245fa, HFC-365mfc, and HCFC-22. However, these may not allow for optimal performance in current foam formulations.
For foams used in various market segments, for example the appliance and water heater markets, the blowing agent must produce rigid foams with good insulating values, i.e., low thermal conductivities (low k-factors). Water heaters and refrigerators both must conform to energy requirements established by the U.S. Department of Energy. Additionally, it is anticipated that these requirements will become even more stringent in the future.
As a direct replacement for HCFC-141b in an appliance foam formulation, third generation blowing agents yield rigid foam in which there is a small to moderate increase in k-factors. The choice of silicone surfactant in the formulation has a direct impact upon the magnitude of this increase in k-factor. That is, the proper choice of surfactant can minimize the potential loss in insulating capability of the foam when converting to a third generation blowing agent.
A variety of papers have been published which discuss the general topic of third generation HFC/HCFC blowing agents and their inferior insulating capability when compared with CFC-11 or HCFC-141b. One, for example, is Barthlemey, P. P.; Leroy, A.; POLYURETHANE 1995 Proceedings of the Polyurethanes 1995 Conference, September, 1995, pp. 26-33.
Bogdan, M. C.; Williams, D. J.; Logsdon, P. B.; Parker, R. C.; Proceedings of Polyurethanes EXPO '96, October, 1996, pp. 394-403. This paper discusses the importance of surfactant choice for optimization of k-factor in rigid polyurethane foam. It lists several surfactants which have been tested in foams made with HFC-245fa as the blowing agent. Furthermore, it concludes that Th. Goldschmidt's B8404 and B8462 and OSi's L-6900 are the best performing silicone surfactants identified to date for improving the foam quality in HFC-245fa-blown foam, including the k-factor and % closed cell content. These polyether-polysiloxane copolymer surfactants each have a calculated total surfactant molecular weight, based on NMR structural analysis, of &lt;10,000 g/mole.
Bodnar, T. W.; Koch, J. J.; Thornsberry, J. D., "New Surfactant Technology for HCFC-123 and HCFC-141b Blown Rigid Foam Systems", Polyurethane World Congress 1991, pp. 24-26 discusses surfactants to optimize rigid foam properties using traditional rigid foam surfactants.
U.S. Pat. Nos. 5,461,084 and 5,426,127 teach the use of HFC blowing agents and B-8426 silicone surfactant in rigid polyurethane foam for low k-factor and good physical properties.
U.S. Pat. No. 4,997,706 teaches the use of C2-C6 polyfluorocarbon compounds containing no Cl or Br atoms as physical blowing agents for rigid closed cell polymer foams. The benefit is that the loss in thermal insulation performance with time compared to foams made in absence of these compounds is reduced.
U.S. Pat. No. 5,432,206 discloses silicone surfactants for making stable polyurethane foam.
U.S. Pat No. 5,525,640 teaches the use of certain surfactants for polyurethane foam made with an inert gas blowing agent.